AbstractAn apparatus, referred to as the microwave kinetics reactor (MWKR), incorporating a microwave‐transparent pressure vessel with mechanical mixing together with a microwave temperature controller, was developed and tested. Experiments were performed to determine a safe and practical operating envelope for the MWKR. Temperatures measured at the center and at the top surface of varying viscosity solutions in the MWKR were used to determine the adequacy of mixing when the solutions were heated from room temperature to 120 °C and held for a prescribed period of time. The viscosities of the solutions were adjusted by adding (carboxymethyl)cellulose (CMC) to distilled water. A 2 CMC solution represented the upper viscosity limit to be heated homogeneously in the apparatus (approximately 2000 cP). To illustrate the usefulness of this apparatus in obtaining kinetic parameters, thiamin hydrochloride degradation kinetics in pea puree were determined at 100, 120, and 130 °C and compared to those obtained from the literature. The MWKR offers an attractive, efficient, convenient, and accurate alternative for the study of reaction kinetics in viscous fluids and semisolids because of its short come‐up time and mixing capability. Experimentally determined kinetic parameters compared very well to those obtained from the literature. As expected the kinetics was first‐order, with an activation energy,Ea, of 27.0 k
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